Showing papers by "University of Antwerp published in 1996"

The tanh method: I. Exact solutions of nonlinear evolution and wave equations

Abstract: A systemized version of the tanh method is used to solve particular evolution and wave equations. If one deals with conservative systems, one seeks travelling wave solutions in the form of a finite series in tanh. If present, boundary conditions are implemented in this expansion. The associated velocity can then be determined a priori, provided the solution vanishes at infinity. Hence, exact closed form solutions can be obtained easily in various cases.

Estimation of the mutation frequencies in Charcot-Marie-Tooth disease type 1 and hereditary neuropathy with liability to pressure palsies: a European collaborative study

Abstract: A European collaboration on Charcot-Marie-Tooth type 1 (CMT1) disease and hereditary neuropathy with liability to pressure palsies (HNPP) was established to estimate the duplication and deletion frequency, respectively, on chromosome 17p11.2 and to make an inventory of mutations in the myelin genes, peripheral myelin protein 22 (PMP22), myelin protein zero (MPZ) and connexin 32 (Cx32) located on chromosomes 17p11.2, 1q21-q23 and Xq13.1, respectively. In 70.7% of 819 unrelated CMT1 patients, the 17p11.2 duplication was present. In 84.0% of 156 unrelated HNPP patients, the 17p11.2 deletion was present. In the nonduplicated CMT1 patients, several different mutations were identified in the myelin genes PMP22, MPZ and Cx32.

A Quantitative Map of Nucleotide Substitution Rates in Bacterial rRNA

Abstract: A recently developed method for estimating the variability of nucleotide sites in a sequence alignment [Van de Peer, Y., Van der Auwera, G. and De Wachter, R. (1996) J. Mol. Evol. 42, 201-210] was applied to bacterial 16S, 5S and 23S rRNAs. In this method, the variability of each nucleotide site is defined as its evolutionary rate relative to the average evolutionary rate of all the nucleotide sites of the molecule. Spectra of evolutionary rates were calculated for each rRNA and show the fastest evolving sites substituting at rates more than 1000 times that of the slowest ones. Variability maps are presented for each rRNA, consisting of secondary structure models where the variability of each nucleotide site is indicated by means of a colored dot. The maps can be interpreted in terms of higher order structure, function and evolution of the molecules and facilitate the selection of areas suitable for the design of PCR primers and hybridization probes. Variability measurement is also important for the precise estimation of evolutionary distances and the inference of phylogenetic trees.

The tanh method: II. Perturbation technique for conservative systems

Abstract: With the aid of the tanh method, nonlinear wave equations are solved in a perturbative way. First, the KdVBurgers equation is investigated in the limit of weak dispersion. As a result, a general shock wave profile, with a perturbative solitary-wave contribution superposed, emerges. For a particular choice of the parameters, a comparison with the exact solution is made. Further, the MKdVBurgers is investigated in the same limit and similar results are obtained.

A Further Augmentation of the Solow Model and the Empirics of Economic Growth for OECD Countries

Abstract: Mankiw, Romer, and Weil [1992] showed that the augmented Solow model, including accumulation of human as well as physical capital, provides a good description of cross-country data, with the exception of the OECD subsample. The textbook Solow model explains about 60 percent of the cross-country variation in per worker GDP in a comprehensive sample of 98 nonoil-producing countries. By including human capital, the augmented Solow model accounts for almost 80 percent of the variation in this sample. For the OECD subsample, explanatory power of the models is rather poor. The textbook Solow model explains very little of the variation in per capita income levels (less than 6 percent). The performance of the Mankiw-Romer-Weil [1992] human capital augmented model is somewhat better but still less than 30 percent. Differences in explanatory power between samples largely disappear in specifications that allow for departures from the steady state. Mankiw, Romer, and Weil interpret this finding by conjecturing that OECD countries are perhaps farther from their steady-state levels than countries in the broader sample. The difference in explanatory power of the augmented Solow model in a broader sample versus the OECD sample is possibly due to the similarity of the OECD countries and the limited variation in explanatory variables. An alternative explanation offered here is that not all relevant factors of production are included. We therefore suggest a further augmentation of the Solow model by explicitly including the (endogenous) accumulation of technological know-how.

Myocardial Contractile Response to Nitric Oxide and cGMP

Abstract: Background Cardiac endothelium releases a number of factors that may modulate performance of underlying cardiac muscle. Nitric oxide (NO), which accounts for the biological activity of the vascular endothelium-derived relaxing factor and relaxes vascular smooth muscle by elevating intracellular cGMP, may be involved in this cardiac modulation. Methods and Results We examined the myocardial contractile effects of the NO-releasing nitrovasodilators sodium nitroprusside (SNP), 3-morpholino-sydnonimine (SIN-1), and S-nitroso-N-acetyl-penicillamine (SNAP); of a cGMP analogue, 8-bromo-cGMP; and of the cGMP-phosphodiesterase inhibitor zaprinast in isolated cat papillary muscle. Modulation of these effects by endocardial endothelium (EE) and by cholinergic and adrenergic stimulation was also investigated. Concentration-response curves with addition of NO-releasing nitrovasodilators (SNP, SIN-1, SNAP) and 8-bromo-cGMP resulted in a biphasic inotropic response. Although administration of low concentrations induced ...

Ceo Locus of Control and Small Firm Performance: an Integrative Framework and Empirical Test*

Abstract: Previous research on the impact of chief executive officer (CEO) locus of control is mainly based on simple and partial mappings of bivariate associations between CEO locus of control and organizational outcomes. In addition, distinct substreams have emerged in which intricately related phenomena are studied separately. To overcome this fragmentation and polarization, we provide and empirically test an integrative framework based on previously tested hypotheses on the impact of CEO locus of control. Our approach differs from prior research in two ways. First, it simultaneously takes account of strategic choice and firm performance in order to assess the extent to which strategy mediates the relationship between CEO locus of control and organizational performance. Second, we consider the CEO to be both a formulator and implementor of organizational strategies. Besides the observation that CEO locus of control seems to matter a lot in terms of explaining organizational performance in the present sample, our results demonstrate that an integrative approach increases our insight into the impact of CEO locus of control by revealing why some CEOs achieve higher organizational performance than others.

Tuning and test of fragmentation models based on identified particles and precision event shape data

Abstract: Event shape and charged particle inclusive distributions are measured using 750000 decays of the Z to hadrons from the DELPHI detector at LEP. These precise data allow a decisive confrontation with models of the hadronization process. Improved tunings of the JETSET, ARIADNE and HERWIG parton shower models and the JETSET matrix element model are obtained by fitting the models to these DELPHI data as well as to identified particle distributions from all LEP experiments. The description of the data distributions by the models is critically reviewed with special importance attributed to identified particles.

Interlaboratory trial on the determination of the In Vitro iron dialysability from food

Abstract: An in vitro method for the estimation of iron bioavailability was subjected to an interlaboratory trial The method involved a simulated gastrointestinal digestion using pepsin for the gastric stage followed by pancreatin and bile salts for the intestinal stage The proportion of iron diffused through a semipermeable membrane (molecular mass cut-off 10 kDa) was used to measure the iron dialysability An interlaboratory trial between nine laboratories was conducted to evaluate the repeatability and reproducibility of the agreed method The reproducibility of the method among the participating laboratories was 20-30% and depended on the content of dialysable iron Several factors contributing to the variation in the in vitro dialysability among laboratories are discussed The pH adjustment in the intestinal digestion was identified as one of the critical parameters The present in vitro method was used to evaluate the iron dialysability from three meals The dialysability data were in reasonable agreement with human absorption data The usefulness of the in vitro dialysability method is discussed

Positional Cloning of a Gene Involved in Hereditary Multiple Exostoses

Abstract: Hereditary multiple exostosis (EXT) is an autosomal dominant condition mainly characterized by the presence of multiple exostoses on the long bones. These exostoses are benign cartilaginous tumors (enchondromata). Three different EXT loci on chromosomes 8q (EXT1), 11p (EXT2) and 19p (EXT3) have been reported, and recently the EXT1 gene was identified by positional cloning. To isolate the EXT2 gene, we constructed a contig of yeast artificial chromosomes (YAC) and P1 clones covering the complete EXT2 candidate region on chromosome 11p11-p12. One of the transcribed sequences isolated from this region corresponds to a novel gene with homology to the EXT1 gene, and harbours inactivating mutations in different patients with hereditary multiple exostoses. This indicates that this gene is the EXT2 gene. EXT2 has an open reading frame encoding 718 amino acids with an overall homology of 30.9% with EXT1, suggesting that a family of related genes might be responsible for the development of EXT.

Transgenic mouse model for the fragile X syndrome.

Abstract: Transgenic fragile X knockout mice have been constructed to provide an animal model to study the physiologic function of the fragile X gene (FMR1) and to gain more insight into the clinical phenotype caused by the absence of the fragile X protein. Initial experiments suggested that the knockout mice show macroorchidism and cognitive and behavioral deficits, abnormalities comparable to those of human fragile X patients. In the present study, we have extended our experiments, and conclude that the Fmr1 knockout mouse is a reliable transgenic model to study the fragile X syndrome. 20 refs., 2 figs., 1 tab.

Low serum levels of alkaline phosphatase of bone origin: a good marker of adynamic bone disease in haemodialysis patients

Abstract: Background. Adynamic bone disease was recently described to be increasingly prevalent in the dialysis population. At present the diagnosis of this type of renal osteodystrophy can only be made by bone histomorphometry. We assessed the value of different biochemical serum markers in the diagnosis of adynamic bone disease. Methods. In 103 haemodialysis patients a bone biopsy was performed after double tetracycline labelling, and the serum levels of intact PTH, osteocalcin, and the bone isoenzyme of alkaline phosphatase were determined. Bone alkaline phosphatase was measured by an optimized agarose gel electrophoretic method, recently shown to have a high accuracy, precision and reproducibility, also in the lower range. Results. In 38 (37%) of the patients the diagnosis of adynamic bone disease was histologically established. Constructing receiver operator curves optimal cut-off levels for the diagnosis of adynamic bone disease were determined, being ≤27 U/litre for the bone isoenzyme of alkaline phosphatase, ≤14 μg/litre for osteocalcin and ≤150 pg/ml for intact PTH. Concentrations of bone alkaline phosphatase or intact PTH below these cut-off levels, were shown to be the best performing tests in the detection of adynamic bone disease as indicated by a sensitivity of 78.1 and 80.6% and a specificity of 86.4 and 76.2% respectively. Applying Bayes' theorema, it was calculated that in the current haemodialysis population in which a prevalence of adynamic bone disease up to 35% has been described, the positive predictive values for the proposed cut-off values are 75% for bone alkaline phosphatase, 65% for intact PTH and 55% for osteocalcin. Moreover, in this population, levels of bone alkaline phosphatase and intact PTH below the optimal cut-off excluded hyperparathyroid bone disease. Conclusion. In view of the relative easy and accurate methodology for bone alkaline phosphatase determination, the closer physiological link with osteoblast function and the lesser expense for its determination we suggest that this marker is a useful tool in the noninvasive diagnosis of the adynamic type of bone disease in the individual patient.

Language Planning as a Discourse on Language and Society: The Linguistic Ideology of a Scholarly Tradition.

Abstract: SAMENVATTINGTaaiplanning als bezinning over taal en maatschappij:de taalkundige ideologie van een geleerde traditieTaalplanning is een traditie die vooral in de jaren 1960 en 1970 bijzonder productief was en in zich een groot optimisme ontwikkelde. De traditie viel wat stil in de jaren 1980, maar kent nu weer een heropbloei, o.m. omwille van de ontwikkelingen in Zuid-Afrika. In deze bijdrage wil ik een evaluatie van de voorbije traditie aansnijden, in het perspectief van de optimalisatie van het theoretisch, conceptueel en methodologisch kader van taalplanning-studies. Ik schets eerst kort de historische ontwikkeling van taalplanning, en ga vervolgens in op enkele ideologische aspecten die in veel traditioneel werk terug te vinden zijn. Ik bespreek achtereenvolgens de courante boutade dat taalplanning geen theoretische achtergrond zou hebben; de intuitieve beperkingen die taaiplanners zich in hun studies leken op te leggen; de organische visies op taal en maatschappij ; het oligolingualisme en de assumpties van efficientie en integratie. Vervolgens vat ik de kritieken van Glyn Williams en Andrew Apter samen. Zij bepleiten een sterkere politieke invalshoek, die taal naast een reeks andere maatschappelijke kenmerken plaatst. Ik sluit af met een pleidooi voor een combinatie van een historiografische en een etnografische benadering in het bestuderen van language planning.RESUMOLingvoplanado kiel debato pri lingvo kaj socio:la lingvistika ideologio de sciencista tradicioLingvoplanado estas tradicio kiu estis tre fekunda cefe en la 1960-aj kaj 1970-aj jaroj kaj kovis en si grandan optimismon. Gi iom fadis en la 1980-aj jaroj, sed nun denove floras, i.a. pro la evoluoj en Suda Afriko. Mi ci tie ekanalizas la tradicion de la pasinteco cele al plibonigo de la teoria, koncepta kaj metodologia kadro de studoj pri lingvoplanado. Mi koncize skizas la historian evoluon de lingvoplanado, kaj poste tusas aron da ideologiaj aspektoj kiujn oni renkontas en multaj el la tradiciaj laboraĵoj. Mi diskutas la aserton ke lingvoplanado ne havus teorian fonon, la intuiciajn limigojn kiujn lingvoplanantoj sajnis starigi al siaj propraj studoj, la organajn konceptojn de lingvo kaj socio, plurlingvismon, kaj la premisojn de efikeco kaj integrado. Mi resumas la kritikojn de Glyn Williams kaj Andrew Apter, kiuj pledas por pli politika aliro en kiu lingvo estas unu el aro da sociaj faktoroj. Fine mi pledas por tio ke en la studado de lingvoplanado oni uzu kombinon el historiografia kaj etnografia aliroj.

Long‐term potentiation in the hippocampus of fragile X knockout mice

Abstract: To gain more insight in the physiological function of the fragile X gene (FMR1) and the mechanisms leading to fragile X syndrome, the Fmr1 gene has been inactivated in mice by gene targeting techniques. In the Morris water maze test, the Fmr1 knockout mice learn to find the hidden platform nearly as well as the control animals, but show impaired performance after the position of the platform has been modified. As malperformance in the Morris water maze test has been associated with impaired long-term potentiation (LTP), electrophysiological studies were performed in hippocampal slices of Fmr1 knockout mice to check for the presence of LTP. Judged by field extracellular excitatory postsynaptic potential recordings in the CA1 hippocampal area, Fmr1 knockout mice express LTP to a similar extent as their wild type littermates during the first 1-2 hr after high frequency stimulation. Also, short-term potentiation (STP) was similar in both types of mice. To investigate whether Fmr1 is involved in the latter stages of LTP as an immediate early gene, we compared Fmr1 mRNA quantities on northern blots after chemical induction of seizures. A transient increase in the transcription of immediate early genes is thought to be essential for the maintenance of LTP. As no increase in Fmr1 mRNA could be detected, neither in cortex nor in total brain, during the first 2 1/2 hr after pentylenetetrazol-induced seizures, it is unlikely that Fmr1 is an immediate early gene in mice. In conclusion, we found no evidence for a function of FMR1 in STP or LTP.

The presenilin genes: a new gene family involved in Alzheimer disease pathology

Abstract: A positional cloning approach has led to the identification of two closely related genes, the presenilins (PS), for autosomal dominant presenile Alzheimer disease (AD): PS-1 at 14q24.3 and PS-2 at 1q31‐q42. The PS-1 gene was identified by direct cDNA selection of yeast artificial chromosomes containing the candidate chromosomal region. Subsequently, the PS-2 gene was identified due to its high sequence homology with PS-1 and its location within the candidate region defined by linkage studies. To date, 30 different missense mutations and one in-frame splice site mutation were described in PS-1, while only two missense mutations were detected in PS-2, suggesting that PS-1 mutations are more frequently involved in familial presenile AD. The PS transcripts encode novel proteins that resemble integral transmembrane proteins of roughly 450 amino acids and at least seven transmembrane domains. The genomic organization of the PS genes is very similar showing that full length PS-1 and PS-2 are encoded by 10 exons. However, different alternative splicing patterns have been observed for PS-1 and PS-2 indicating that the corresponding proteins (ps-1 and ps-2) may have similar but not identical biological functions.

Two-electron quantum disks.

Abstract: The energy levels of a quantum disk containing one or two electrons are calculated as a function of an external magnetic field. The confinement potential is a hard wall of finite height. The cyclotron transition energies are investigated and the effect of the finite width of the disk on the Coulomb energy is studied. Our results are applied to the ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/GaAs dots and agree well with experiment. \textcopyright{} 1996 The American Physical Society.

Detection of Mycoplasma pneumoniae by Two Polymerase Chain Reactions and Role of M. pneumoniae in Acute Respiratory Tract Infections in Pediatric Patients

Abstract: Mycoplasma pneumoniae and viruses in acute respiratory tract infections in children were studied during the winter of 1992-1993 in Antwerp, Belgium. M. pneumoniae was diagnosed in nasopharyngeal aspirates by culture and polymerase chain reaction (PCR). For this, amplification of a fragment of the PI adhesin gene in samples prepared by two methods was compared in two laboratories, and in one laboratory, a fragment of the 16S rRNA gene was amplified. The sensitivity of culture versus PCR was 61.5%. Provided a specific internal control is used, sample preparation by freeze-boiling combined with PCR for the PI gene and amplicon detection by visual inspection of the electrophoresis gel can be recommended, although maximal results are obtained after hybridization. M. pneumoniae was present in 0.5% of patients 2. M. pneumoniae was second to respiratory syncytial virus or detected equally in lower respiratory infections.